Power over Ethernet (PoE), which is outlined in IEEE Std 802.3™-2005 clause 33 (the PoE standard), refers to a technique for delivering power and data to an electronic device via Ethernet cabling. In a PoE system, a power sourcing equipment (PSE) device provides a power supply to electronic devices, which may be referred to as powered devices, via an Ethernet cable. PoE eliminates the need for a separate power source to deliver power to attached powered devices. Such powered devices may include Voice over Internet Protocol (VoIP) telephones, wireless routers, security devices, field devices to monitor process control parameters, data processors, other electronic devices, or any combination thereof.
In general, the PoE standard requires each of the Ethernet ports associated with a powered device (i.e., an electronic device that receives both power and data from the Ethernet cable) to be electrically isolated from any other conductor that is user accessible, including a metal housing, a display, a touch screen, a switch, a screw, another connector, or any combination thereof. Conventionally, powered devices are isolated using direct-current-to-direct-current (DC-to-DC) converters without a physical connection from the input to the output. For example, particular implementations of forward and flyback switch topologies may utilize a transformer to isolate a PoE interface of the powered device from the rest of its circuitry while also transforming a PoE input voltage to a voltage level that is suitable for powering circuitry of the powered device. Another conventional method of achieving voltage isolation in a PoE environment uses a power converter that includes a transformer and an opto-isolated output voltage feedback to regulate the output voltage. However, such conventional PoE isolation circuitry may use an external reference voltage, which requires additional circuitry. In some instances, such conventional PoE isolation circuitry may also utilize large external capacitors and external opto-isolation devices to provide isolation at a feedback path. Such external devices may increase overall power consumption and circuit costs.